Datasheet

_
+
V
DD
V
O+
V
O−
GND
6
5
8
7
To Battery
C
s
IN−
IN+
4
3
+
−
In From
DAC
R
I
R
I
40 kΩ
40 kΩ
(1)
C
(BYPASS)
is optional
Bias
Circuitry
2
SHUTDOWN
1
C
(BYPASS)
(1)
100 kΩ
TPA6211A1
www.ti.com SLOS367D –AUGUST 2003– REVISED JUNE 2011
APPLICATION INFORMATION
mid-supply voltage affects both positive and
negative channels equally, thus canceling at the
FULLY DIFFERENTIAL AMPLIFIER
differential output. Removing the bypass capacitor
The TPA6211A1 is a fully differential amplifier with
slightly worsens power supply rejection ratio
differential inputs and outputs. The fully differential
(k
SVR
), but a slight decrease of k
SVR
may be
amplifier consists of a differential amplifier and a
acceptable when an additional component can be
common- mode amplifier. The differential amplifier
eliminated (See Figure 17).
ensures that the amplifier outputs a differential
• Better RF-immunity: GSM handsets save power
voltage that is equal to the differential input times the
by turning on and shutting off the RF transmitter at
gain. The common-mode feedback ensures that the
a rate of 217 Hz. The transmitted signal is
common-mode voltage at the output is biased around
picked-up on input and output traces. The fully
V
DD
/2 regardless of the common- mode voltage at the
differential amplifier cancels the signal much
input.
better than the typical audio amplifier.
Advantages of Fully Differential Amplifiers
APPLICATION SCHEMATICS
• Input coupling capacitors not required: A fully
differential amplifier with good CMRR, like the Figure 28 through Figure 31 show application
TPA6211A1, allows the inputs to be biased at schematics for differential and single-ended inputs.
voltage other than mid-supply. For example, if a Typical values are shown in Table 1.
DAC has a lower mid-supply voltage than that of
the TPA6211A1, the common-mode feedback Table 1. Typical Component Values
circuit compensates, and the outputs are still
COMPONENT VALUE
biased at the mid-supply point of the TPA6211A1.
R
I
40 kΩ
The inputs of the TPA6211A1 can be biased from
C
(BYPASS)
(1)
0.22 μF
0.5 V to V
DD
- 0.8 V. If the inputs are biased
outside of that range, input coupling capacitors
C
S
1 μF
are required.
C
I
0.22 μF
• Mid-supply bypass capacitor, C
(BYPASS)
, not
required: The fully differential amplifier does not
require a bypass capacitor. Any shift in the (1) C
(BYPASS)
is optional.
Figure 28. Typical Differential Input Application Schematic
Copyright © 2003–2011, Texas Instruments Incorporated 13